Method of electroplating cadmium on cadmium-zinc alloys



April 28, 1936. E Q DOMM 2,038,550

METHOD oF ELEGTROPLATING CADMIUM oN CADMIUM-ZINC ALLoYs Filed oct. 31,1934 ferrous Ue/'re @@WM@ @www Patented Apr. 28, 1936 UNITED vSTATESMETHOD OF ELECTROPLATING CADMIUM ON `CADMUltI-ZINC ALLOYS ElginCarletonDomm, Niles, Mich., assignor to National-Standard Company,vNiles, Mich., a corporation of Michigan Application October 31, 1934,Serial No. -750,874

8 Claims.

'I'his invention relates to improvements in a method of coatingmetal.

This application is a continuation-impart of my co-pending applicationSerial No. 653,549, filed January 25, 1933.

In the Crapo patent No. 1,984,335 issued Dec. 11, 1934, is described amethod of coating a ferrous article by hot-galvanizing it with zinc, andover that depositing by some other method an additional coating ofcadmium. Y

It has now been discovered that in those methods the thickness of theundercoating may be decreased without injuring corrosion-resistance tothe type of corrosion of which salt-spray is typical, if instead of thezinc under-coating an alloy of cadmium and zinc is used for suchunder-coating. At the same time, such an alloy may be applied at a lowertemperature, and thus may be used .in certain instances where theapplication of zinc alone by the hot-dip method might interfere with thecharacter of the base.

The invention is particularly applicable to coating strands of wire tobe used in reinforcing the bead of a tire. 'I'he wire when so usedcommonly acts as a tension-member, and is imbedded in a rubber or rubbercompound. When i so used, the wire is exposed tocorrosive and rustingagents, particularly to moisture which may seep into the tire.

The drawing shows in diagrammatic form an embodiiifnt of my invention.

In ac ordance with the invention, aemetal, for example wire suitablefor' use in tire beads, is first hot-dipped to provide a coating of acadmium-zinc alloy. This may be done, for example, by dipping the wirein a hot molten alloy of zinc and cadmium. Such an alloy always has amelting point 'lower than-that of zinc. and certain of the alloys have'a melting point below that of either zinc or cadmium.-

A coating of cadmium is then putover the rst coat by electrolysis orelectroplatlng. Not only does a double coating applied by the abovementioned method give very good 'corrosion-resistance, but it has rtro-coat tends to ll in the depressions in the lower zinc-cadmium alloycoat and thus produce a uniform and smoothcoating. A coating of theorder of thickness of the lower coat is preferred.

, may be applied If desired, copper or. other suitable material over thecorrosive-resistant double coating in order to increase the adhesivenessof the 'wire tovrubber. It is frequently desirable to apply such acoating when wire is used as a reinforcement fora tire bead. 4

, The new process herein described is especially usefulln procuring acoating of a desired and uniform thickness. In practice, the wire isgiven a hot coat ilrst, and preferably! wipe this thin. In the nextstage. the coating is put on by elecbeen discovered that the elec- (C1.sii-) troplating;` the operation can be continued to give exactly adesired thickness. time, the coating acquires a smooth, uniformcharacter which is freefrom holes, defects, and the like.

As an example of the invention, it is preferred to use an alloy ofapproximately zinc and 20% cadmium as the undercoating, because of itsmarked corrosion-resistance to the type of corrosion of which the saltspray is typical.

In general it is preferred that the alloy contain at least 10% cadmiumand at least 30% of zinc.

The foregoing description has been given for clearness of understandingonly, and no unnecessary limitations should be understood therefrom, butthe appended claims should be construed as broadly as permissible'inview of the prior art.

What I regard as new and desire to Letters Patent is:

l. 'Ihe process of coating a ferrous article which comprises applying;toit by the hot-dip secure by At the same zinc, and electro-depositingthereon an outer coating of cadmium.

2. The method of coating a metal to increase its corrosion-resistancecomprising rst applying to it a molten zinc-cadmium alloy, and thenapplying a second coating of cadmiuml over the first coating.

3. 'Ihe method of producing-a ferrous tirebead reinforcement wire whichcomprises ilrst coating a ferrous wire with a zinc-cadmium alloy by thehot-dip process, and then electroplating cadmium over the hot-dippedwire to produce a uniform coating" of desired thickness.

4. 'I'he method as set forth in claim 1, in which 'the zinc-cadmiumalloy contains approximately 80 parts of zinc to 20 parts of cadmium.

5. A coated ferrous article, comprising a ferrous base 'having ahot-dipped coating of a zinccadmium alloy thereon, and over that anelectrodeposited coating substantially wholly of cadmium. 6- A coatedferrous wire comprising a ferrous base wire having a hot-dipped coatingof a cadmium-zinc alloy thcreomand over that an electrodeposited coatingsubstantially wholly of cad- 7. A' coated ltire bead wirecomprising aferrous base wire having a hot-dipped coating of a zinc-cadmium alloythereon, and electrodeposited coating substantially wholly of cadmiumthereon, and having a coating of rubber vulcanized thereto. l

8. An article as set forth in claim 5, in which the zinc-cadmium alloycontains approximately 80partszinpto20partscadmium.

ELGIN CARIEI'ON DOIN.

